1. Field of Application
The present invention relates to a knock sensor signal processing apparatus which performs A/D (analog-to-digital) conversion and digital filter processing of respective sensor signals produced from one or more knock sensors of an internal combustion engine.
2. Description of Related Art
Types of apparatus are known for use in controlling the engine of a vehicle whereby during each of successive intervals, a judgement is made as to whether knocking is occurring in a cylinder of the engine. The judgement is based upon an analog signal (referred to in the following as a knock sensor signal) produced from a knock sensor that is installed in the engine, with the knock sensor signal being subjected to A/D conversion at fixed periodic intervals. Digital filter processing is applied to the resultant train of digital values and a decision as to whether knocking is occurring in a cylinder is made based upon the results of the digital filter processing.
In the following description and appended claims, a digital value resulting from an A/D conversion operation is referred to simply as an “A/D value”.
Such a form of knock judgement is described for example in Japanese patent first publication No. 2004-309267 (referred to in the following as reference document 1).
A signal processing apparatus for performing such A/D conversion and digital filter processing of a knock sensor signal can for example be based on a first apparatus that includes an A/D converter which operates on the knock sensor signal and a second apparatus which acquires resultant A/D values from the first apparatus at periodic fixed intervals, transmitted via a communication line, with the second apparatus performing digital filter processing of the series of sensor A/D values and knock judgement based on the filtering results. With such a system, the second apparatus may transmit commands to the first apparatus that include request commands for designating respective A/D conversions to be performed (with these commands being sent at fixed periodic intervals). Each time that the first apparatus receives such an A/D conversion request command, it transmits an A/D value obtained from the A/D converter, to the second apparatus. A/D values are thereby transmitted from the first apparatus to the second apparatus at regular intervals. Such a system has been described by the assignees of the present invention, in Japanese patent first publication No. 2006-112346.
Furthermore in recent years there has been an increasing tendency for the level of electrical noise within a motor vehicle to increase, as the number of functions performed by equipment of vehicles continues to increase. For that reason, in order to reduce the effects of noise interference upon the accuracy of knock judgement processing, it has been proposed to utilize the high-frequency components of a knock sensor signal for purposes of knock judgement, instead of the peak values of the basic low-frequency components of that signal. This is described for example in Japanese patent first publication No. 2004-317207 (referred to in the following as reference document 2).
In order to utilize high-frequency components of a knock sensor signal in performing knock judgement, with that judgement being performed by digital signal processing, it is necessary to utilize a high-speed A/D converter for digitizing the knock sensor signal, i.e., the sampling period of the knock sensor signal must be made short.
If the frequency components of the knock sensor signal that are to be utilized in knock judgement are below approximately 20 kHz, then the sampling frequency, i.e., 1/(sampling period), should be set at approximately 100 kHz. However if it is required to utilize frequency components of up to 40 kHz, then the sampling frequency must correspondingly be made substantially high, i.e., approximately 200 kHz. This is necessary since if a 40 kHz signal is sampled at a frequency of 200 kHz, then only 2 to 3 sample values would be obtained in each sampling period. Hence if high-frequency components of knock sensor signal are to be used in knock judgement, it is essential to make the sampling frequency used for A/D conversion of the knock sensor signal correspondingly high.
However if a knock sensor signal processing apparatus such as described in reference document 1 or reference document 2 is used (that is, in which a first apparatus performs A/D conversion of a knock sensor signal and a second apparatus performs digital signal processing of the resultant converted values) and the sampling period of the A/D conversion is made short, then the number of A/D converted values (referred to in the following simply as A/D values) that must be transferred from the first apparatus to the second apparatus per unit time interval will increase accordingly.
It might be envisaged that this could be handled by simply increasing the communication speed, i.e., increasing the rate of serial data transfer between the first apparatus and second apparatus. However if this is done, then the electrical noise that is generated as a result of the communication itself will be increased. This is a significant problem.
Alternatively, it might be envisaged that the problem could be overcome by using data bus communication rather than serial data transfer, with respective communication lines provided for each bit of a set of data that are to be transferred concurrently between the first apparatus and second apparatus. However this would result in a substantial increase in the total number of communication lines that must be connected between the first and second apparatuses, and in the number of corresponding connection terminals of these (i.e., when the first and second apparatuses are respective integrated circuits, the number of connector pins of each IC). Hence, the overall system scale would become excessive.